Nuclear Theory·nucl-th

Monday·March 23, 2015

12 papers—9 primary·3 cross-listed

01
Adiabatic hyperspherical analysis of realistic nuclear potentials
K. M. Daily · Alejandro Kievsky · Chris H. Greene
Using the hyperspherical adiabatic method with the realistic nuclear potentials Argonne V14, Argonne V18, and Argonne V18 with the Urbana IX three-body potential, we calculate the adiabatic potentials and the triton bound state energies. We find that a discrete variable representation with the slow variable discretization method along the hyperradial degree of freedom results in energies consistent with the literature. However, using a Laguerre basis results in missing energy, even when extrapolated to an infinite number of basis functions and channels. We do not include the isospin $T = 3/2$ contribution in our analysis.
nucl-thFew Body Syst.(2015)·7 citations
02
Dynamics of two-cluster systems in phase space
Yu. A. Lashko · G.F. Filippov · V.S. Vasilevsky
We present a phase-space representation of quantum state vectors for two-cluster systems. Density distributions in the Fock--Bargmann space are constructed for bound and resonance states of $^{6, 7}$ Li and $^{7, 8}$ Be, provided that all these nuclei are treated within a microscopic two-cluster model. The density distribution in the phase space is compared with those in the coordinate and momentum representations. Bound states realize themselves in a compact area of the phase space, as also do narrow resonance states. We establish the quantitative boundaries of this region in the phase space for the nuclei under consideration. Quantum trajectories are demonstrated to approach their classical limit with increasing energy.
nucl-thquant-phNPA(2015)·8 citations
03
Reappraisal of the limit on the variation in $α$ implied by Oklo
Edward D. Davis · Leila Hamdan
We reconsider the analysis of the sensitivity of neutron resonance energies $E_{i}$ to changes in $α$ with a view to resolving uncertainties that plague earlier treatments. We point out that, with more appropriate choices of nuclear parameters, the standard estimate (due to Damour and Dyson) of the sensitivity for resonances in $^{150}$ Sm is increased by a factor of 2.5. We go on to identify and compute excitation, Coulomb and deformation corrections. To this end, we use deformed Fermi density distributions fitted to the output of Hartree-Fock (HF) + BCS calculations (with both the SLy4 and SkM $^{*}$ Skyrme functionals), the energetics of the surface diffuseness of nuclei, and thermal properties of their deformation. We also invoke the eigenstate thermalization hypothesis, performing the requisite microcanonical averages with two phenomenological level densities which, via the leptodermous expansion of the level density parameter, include the effect of increased surface diffuseness. Theoretical uncertainties are assessed with the \emph{inter-model} prescription of Dobaczewski et al. [J. Phys. G: Nucl. Part. Phys. {\bf 41}, 074001 (2014)]. The corrections diminish the revised $^{150}$ Sm sensitivity but not by more than 25\%. Subject to a weak and testable restriction on the change in $m_{q} /Λ$ (relative to the change in $α$ ) since the time when the Oklo reactors were active ( $m_{q}$ is the average of the $u$ and $d$ current quark masses, and $Λ$ is the mass scale of quantum chromodynamics), we deduce that $∣ α_{Oklo} - α_{now} ∣ < 1.1 \times 1 0^{- 8} α_{now}$ (95\% confidence level). The corresponding bound on the present-day time variation of $α$ is tighter than the best limit to date from atomic clock experiments.
nucl-thastro-ph.COgr-qcPRC(2015)·17 citations
04
Kinetic evolution and correlation of fluctuations in an expanding quark gluon plasma
Golam Sarwar🇮🇳 · Jan-e Alam🇮🇳
Evolution of spatially anisotropic perturbation created in the system formed after Relativistic Heavy Ion Collisions has been studied. The microscopic evolution of the fluctuations has been examined within the ambit of Boltzmann Transport Equation (BTE) in a hydrodynamically expanding background. The expansion of the background composed of Quark Gluon Plasma (QGP) is treated within the framework of relativistic hydrodynamics. Spatial anisotropic fluctuations with different geometry have been evolved through Boltzmann equation. It is observed that the trace of such fluctuation survive the evolution. Within the relaxation time approximation analytical results have been obtained for the evolution of these anisotropies. Explicit relations between fluctuations and transport coefficients have been derived. The mixing of various Fourier (or $k$ ) modes of the perturbations during the evolution of the system has been explicitly demonstrated. This study is very useful in understanding the presumption that the measured anisotropies in the data from heavy ion collisions at relativistic energies imitate the initial state effects. The evolution of correlation function for the perturbation in pressure has been studied and shown that the initial correlation between two neighbouring points in real space evolves to a constant value at later time which gives rise to Dirac delta function for the correlation function in Fourier space. The power spectrum of the fluctuation in thermodynamic quantities (like temperature estimated in this work) can be connected to the fluctuation in transverse momentum of the thermal hadrons measured experimentally. The bulk viscous coefficient of the QGP has been estimated by using correlations of pressure fluctuation with the help of Green-Kubo relation. Angular power spectrum of the anisotropies has been estimated in the appendix.
nucl-thhep-phInt.J.Mod.Phys.A(2018)·9 citations
05
Investigation of $K^{ba r} N N$ resonances with a coupled-channel Complex Scaling Method + Feshbach projection
Akinobu Doté🇯🇵 · Takashi Inoue🇯🇵 · Takayuki Myo🇯🇵
We have investigated a prototype of kaonic nuclei, " $K^{-} pp$ ", with a coupled-channel Complex Scaling Method (ccCSM). Combining the ccCSM with Feshbach projection method, we can handle a coupled-channel problem effectively as a single-channel problem. By using an energy-dependent chiral SU(3)-based $K ˉ N$ potential, the $K^{-} pp$ ( $J^{π} = 0^{-}$ and $T = 1/2$ ) is obtained to be shallowly bound with the binding energy of 20-30 MeV. The mesonic decay width depends on the interaction parameters and ansatz; the decay width is ranging from 20 to 65 MeV. In case of $J^{π} = 1^{-}$ state, no three-body $K ˉ N N$ resonant states are found.
nucl-thnucl-exHyperfine Interact.(2015)·2 citations
06
Extracting the Mass Dependence and Quantum Numbers of Short-Range Correlated Pairs from A(e,e'p) and A(e,e'pp) Scattering
C. Colle · O. Hen · W. Cosyn · I. Korover · E. Piasetzky · J. Ryckebusch · L.B. Weinstein
The nuclear mass dependence of the number of short-range correlated (SRC) proton-proton (pp) and proton-neutron (pn) pairs in nuclei is a sensitive probe of the dynamics of short-range pairs in the ground state of atomic nuclei. This work presents an analysis of electroinduced single-proton and two-proton knockout measurements off 12C, 27Al, 56Fe, and 208Pb in kinematics dominated by scattering off SRC pairs. The nuclear mass dependence of the observed A(e,e'pp)/12C(e,e'pp) cross-section ratios and the extracted number of pp- and pn-SRC pairs are much softer than the mass dependence of the total number of possible pairs. This is in agreement with a physical picture of SRC affecting predominantly nucleon-nucleon pairs in a nodeless relative-S state of the mean-field basis.
nucl-thnucl-exPRC(2015)·63 citations
07
Studying short-range correlations and momentum distributions with unitarily transformed operators
Thomas Neff · Hans Feldmeier · Wataru Horiuchi · Dennis Weber
Short-range correlations in 4He are investigated using many-body wave functions obtained in the no-core shell model. The similarity renormalization group (SRG) is used to evolve the Argonne V8' interaction and the density operators. The effects of short-range correlations are reflected in the two-body densities in coordinate space as a function of the distance between two nucleons, or alternatively in in momentum space as function of the relative momentum between two nucleons. The SRG transformation is performed in two-body approximation. The importance of missing three-body and higher-body contributions is investigated by comparing results obtained for different flow parameters and by comparing to exact results with the bare Argonne V8' interaction obtained in the correlated Gaussian approach.
nucl-thJPS Conf.Proc.(2015)·1 citation
08
The Non-Mesonic Weak Decay of Double-Lambda Hypernuclei: A Microscopic Approach
E. Bauer🇦🇷 · G. Garbarino🇮🇹 · C. A. Rodriguez Peña🇦🇷
The non--mesonic weak decay of double-- $Λ$ hypernuclei is studied within a microscopic diagrammatic approach. Besides the nucleon--induced mechanism, $Λ N \to n N$ , widely studied in single-- $Λ$ hypernuclei, additional hyperon--induced mechanisms, $ΛΛ \to Λ n$ , $ΛΛ \to Σ^{0} n$ and $ΛΛ \to Σ^{-} p$ , are accessible in double-- $Λ$ hypernuclei and are investigated here. As in previous works on single-- $Λ$ hypernuclei, we adopt a nuclear matter formalism extended to finite nuclei via the local density approximation and a one--meson exchange weak transition potential (including the ground state pseudoscalar and vector octets mesons) supplemented by correlated and uncorrelated two--pion--exchange contributions. The weak decay rates are evaluated for hypernuclei in the region of the experimentally accessible light hypernuclei $_{ΛΛ}^{10}$ Be and $_{ΛΛ}^{13}$ B. Our predictions are compared with a few previous evaluations. The rate for the $ΛΛ \to Λ n$ decay is dominated by $K$ --, $K^{*}$ -- and $η$ --exchange and turns out to be about 2.5\% of the free $Λ$ decay rate, $Γ_{Λ}^{free}$ , while the total rate for the $ΛΛ \to Σ^{0} n$ and $ΛΛ \to Σ^{-} p$ decays, dominated by $π$ --exchange, amounts to about 0.25\% of $Γ_{Λ}^{free}$ . The experimental measurement of these decays would be essential for the beginning of a systematic study of the non--mesonic decay of strangeness $- 2$ hypernuclei. This field of research could also shed light on the possible existence and nature of the $H$ --dibaryon.
nucl-th0 citations
09
Study of nuclear pairing with Configuration-Space Monte-Carlo approach
Mark Lingle · Alexander Volya
Pairing correlations in nuclei play a decisive role in determining nuclear drip-lines, binding energies, and many collective properties. In this work a new Configuration-Space Monte-Carlo (CSMC) method for treating nuclear pairing correlations is developed, implemented, and demonstrated. In CSMC the Hamiltonian matrix is stochastically generated in Krylov subspace, resulting in the Monte-Carlo version of Lanczos-like diagonalization. The advantages of this approach over other techniques are discussed; the absence of the fermionic sign problem, probabilistic interpretation of quantum-mechanical amplitudes, and ability to handle truly large-scale problems with defined precision and error control, are noteworthy merits of CSMC. The features of our CSMC approach are shown using models and realistic examples. Special attention is given to difficult limits: situations with non-constant pairing strengths, cases with nearly degenerate excited states, limits when pairing correlations in finite systems are weak, and problems when the relevant configuration space is large.
nucl-th0 citations

Affiliations

first authorsco-authorsvia INSPIRE